Percussion tool



June 11, w68 s. L. COLLIER PERCUSSION TOOL 6 Sheets-Sheet l Filed OC'L. l5, 1965 Jcwyf/e/ COM/@ INVENTOR. 2a

Afro/m5 y I June 11, 1968 s. COLLIER PERCUSSION TOOL 6 Sheets-Sheet 2 Filed Oct. l5, 1965 f M MR. .W w, 0 E NX am .f A M d. e n4 a n Y@ a B 0U June 11, 1968 s. l.. COLLIER 3,387,671

PERCUSS I ON TOOL Filed OCCY l5, 1965 6 Sheets-Sheet 5 s f s LN L?? L s /j s f@ s [|50 l/ s as y 55; I; Jamae/ Z. a/l///4 `lune l1, 1968 Filed Oct. l5, 1965 S. l COLLIER PERCUSSION TOOL 6 Sheets-Sheet 4 INVENTOR.

June 11, 1968 s. L. COLLIER 3,387,671

PERCUSSION TOOL Filed Oct. l5, 1965 6 Sheets-Sheet 5 I /a f,

Jamue/ (c7/her INVENTOR.

I I BYl ,Q l

June 11, 1968 s. L. COLUER PERCUSSION TOOL 6 Sheets-Sheet 6 Filed Oct. l5, 1965 Jll ATTOR/VEV United States Patent O ABSTRACT F THE DISCLOSURE A downhole type of percussion drilling tool particularly adapted for operation by the pumped drilling mud or other pressured liquid, including a reciprocating differential piston having a single, double-seating valve between the downstream face of the piston and the abutting anvil face.

This invention relates to percussion motors for operating rock drills particularly of the downhole type and utilizing either liquid, such as drilling mud, or gaseous motivating uid.

Various liquid-operated tools heretofore devised have been of complicated design and have utilized a multiplicity of complicated parts. Sometimes the operating cycles of these tools have caused undesirable vibrations of the ambient fluid in the well, as well as inordinately high mechanical vibrations. Also, such designs have embodied heavy hammers and relatively small working areas because of the lilling of the available tool space with cornplex iiow passages and mechanisms. Thus, higher working pressures are necessary with resultant increases in surge or shock pressures. Finally, previous tools have not been able to utilize both gaseous and liquid working uids supplied at widely varying pressures and volumes, particularly drilling mud at pressures as high as tive hundred pounds per square inch.

Accordingly, an object or the present invention is to provide a novel percussion drill of the downhole type which is adapted for operation by a liquid, such as the usual drilling mud used for flushing out the debris, lubrieating the bit, sealing the bore wall, and preventing blowouts.

Another object is to provide a percussion drill of the above type in which surge or shock pressures are minimized.

Another object is to provide a percussion drill which is adapted to utilize motivating uids of substantially varying pressures and volumes.

Another object is to provide a percussion drill of the above type which can utilize either liquid or gaseous motivating fluids.

Still another object is to provide a percussion drill the use of which is accompanied by substantial continuity in the upward ow of the ambient drill uid.

These objects and others are attained by the structures illustrated in the accompanying drawings, in which FIG. 1 is a vertical transverse section through a preferred form of the novel percussion drill, just before irnpact;

FIG. 2 is a partial vertical transverse section as in FlG. l, but showing the valves just after impact;

FlG. 3 is a vertical transverse section illustrating a modification of the piston valve seat design;

FIG. 4 is a similar section illustrating a modified valve design;

FIG. 5 is a similar view illustrating another modification;

FIG. 6 is a detail vertical transverse section illustrating a modification in the bumper design;

FIG. 7 is an enlarged vertical central section showing another modified valve arrangement;

3,387,671 Patented `lune 11, 1968 ice FIG. 8 is a view similar to FIG. 7 but showing the valve reversed;

FIG. 9 is a broken section on line 9-9 of FIG. 7;

FIGS. 10-14 inclusive, are partial vertical transverse sectional views in different operative positions and showing another modied valve; and

FIGS. 15 and 16 are similar views of still another valve modilication in different positions.

The novel percussion drill is constructed, in general, of a hollow casing or cylinder which is interposed between the drill bit and drill collars usually provided at the lower end of the tubular drill string which is suspended from the rotary rig into the Well. An anvil is telescopingly and slidably received in the forward (lower) part of the casing, and a hollow piston of differential design is Slidable in the casing above the anvil. The usual exhaust duct extends through the anvil and the bit. A novel, double-acting check valve, which may take various forms, is received between valve seats provided on the adjacent extremities of the anvil exhaust duct and the passage through the piston and is provided with means which, during normal operation, urges the valve rearwardly against the piston in a manner to resist access of the working fluid to the forward working chamber below the piston so that the working fluid will drive the piston downwardly. When the piston strikes the anvil, the valve is driven forwardly by inertia and the force of the motivating uid so as to open the piston valve seat and close the adjacent Valve seat on the anvil exhaust duct. This exposes the lower surface of the piston, which is greater in area than the upper surface of the piston, to the working uid so as to drive the piston rearwardly. During the latter part of the return stroke of the piston, the valve is unseated from the anvil valve seat, either mechanically or hydraulically, and reseated against the piston valve seat, thus initiating another cycle of piston movement.

In FIGS. 1 and 2 there are shown the lower extremity 8 of a drill string to which is threadedly secured an adapter sub 9 to which is, in turn, threadedly secured a generally cylindrical, top piston case or back head member 10. A cylindrical bumper member 11, having an external Y collar 12, is supported from member 10, as by means of longitudinal ribs 13, so that drill motivating uid can pass downwardly around as well as through the bumper.

Cylindrical motor casing 16 is threadedly secured at its rear end to the lower portion of top piston case member 10 and, at its forward extremity, is threadedly secured to driver subnut 17 which, during normal operation, rests upon a shoulder 18 of anvil 19. The anvil shown is threadedly secured to a separate percussion bit 20 but may be formed integrally with the bit. A longitudinal exhaust duct or passage 21 extends through anvil 19 in line with and continuation of exhaust duct extension 22 in the bit. The anvil and casing are provided with externalsplines 23 in which are received roller bearings 24, secured in position by driver subnut 17, for permitting longitudinal movement of the anvil with respect to the casing, While enforcing joint rotation of the casing and the anvil.

Slidable Within casing 16 above the anvil and extending into top piston case member 10 is a hollow, differential hammer piston 26 having an upper portion 27 provided with a sealing ring 28 vwhich is slidably received in member 10. The piston also includes a diametrically larger lower portion 29 having lubricant grooves 30 and a sealing ring 30a slidably received in main casing 16. Preferably, the forwardly-facing area of piston 26 is about twice the rearwardly-facing area thereof. Internal passage 31 in the piston is aligned with internal passage 32 of rbumper 11 and exhaust duct 21 in the anvil. The clearance space 33 in casing 16 between the piston 26 and member 10 is vented by means of passages 34. The clearance is charged with a suitable liuid, preferably a lubricant which is not very miscible with the ambient well uid in the annulus between the drill casing and the well bore. Vents 34 are of adequate capacity with respect to the displacement of rear piston part 27 in space 33 that the ambient well duid will not be pumped into this space during operation of the tool. In other words, such displacement is less than the volume of vents 34. Thus, the parting line between the fluid charge in space 33 will fluctuate in the vents and will not enter the clearance space. Alternatively, the initial immersion of the tool in the hole will lill space 33 with relatively grit-free well iluid.

The forward surface 36 of the piston is provided with a central valve chamber forming countersink 37 having a forwardly-facing shoulder 3S which intersects with the wall of piston passage 31 to form a valve seating clement 35. As shown, this seating element is formed by a sharp corner, but may Vbe formed Yby a wider, chamfered surface, as will be explained. The forward face of the piston is peripherally relieved, as at 54, to accommodate a stop ring S which limits the forward movement of the piston when the tool is hanging off bottom. A one-piece valve 39, at least the surface of which, in whole or in part, preferably, is of suitable resilient material, is received in the valve chamber formed by piston countersink 3? and tbetween piston valve seating element 35 and a valve seating element 4t) -at the upper extremity of exhaust duct Z1 in anvil 19. This seat, preferably, is chamfered, as shown, and may be provided with a resilient seating insert. The valve has a generally cylindrical, skeletonized superstructure 41 provided with an upper flange 42 which is of less radius than internal passage 31 of the hammer piston but radially overlaps a snap ring 43 provided in the wall of passage 31. Ring 43 may have, as shown, a resilient mounting 43a to dissipate some of the shock thereon. A plurality of legs 44 and 45 depend from valve ybody 39, legs 44 resting upon an apertured spring seating disk 46, while center leg 45 extends slidably through the disk and is distally provided with a cotter key 47 or other stop for maintaining the assembly. A coiled compression spring 48 is also received in the enlarged entry part 21a of anvil duct 21 and about spring guiding fingers or sleeve 49 depending from disk 46. Spring 48, at its lower end, seats against a replaceable bushing S0 which rests upon an internal shoulder 51 within exhaust duct 21. The thickness of 'bushing 50 may be varied to vary the prestressing of spring 48.

The percussion motor above described operates as follows: When operating uid is not being supplied through the connection formed by inlet passage 32 at suicient pressure to drive piston 26 downwardly against spring 48 and the ambient well pressure, the piston will be urged upwardly causing its upper surface 51 to engage the under surface of bumper 11. This limits the piston movement under such conditions and, at the same time, since motoring valve 39 will be closed against piston seating element 35, the interior of the motor will be substantially sealed against the upward entry of ambient drill fluid, so that an additional float valve is unnecessary. When operating fluid, either drilling mud or other liquid or gas, is supplied through the drill pipe at suicient pressure such that operating fluid pressure times exposed upwardly-facing piston and valve area (PmX1ra2/4) is greater than the reactive force of spring 48 plus the ambient well pressure times the downwardly-facing piston and valve area (rc2/4), the piston is forced downwardly or forwardly (FIG. l). When the under surface 36 of the piston strikes the upper surface of anvil 19, the inertia of valve 39 plus the operating fluid force thereon causes the free floating valve to move downwardly away from piston seat element 35 and into sealing engagement with anvil seat element 40. The operating fluid now has access between the valve and seating element 35 to the under surfaces 38, 36 of the piston. Since the downwardly- Cil or forwardly-facing surfaces of the piston are greater than the upwardlyor rearwardly-facing surfaces thereof, the piston twill -be caused to move upwardly (rearwardly, FIG. 2). During this return piston stroke, snap ring 43 will engage shoulder 42 on valve superstructure 41, positively unseating the valve body from anvil valve seat 40. The resultant equalization of iiuid pressures across the valve will permit spring 48 to again seat the valve body against the piston valve seat element 35. The pressured operating fluid will now reverse the piston movement and again drive the piston downwardly in its working stroke.

During the rearward movement of the piston, a pulse from fluid trapped in the space 33 between the piston and casing 16 will pass outwardly through ample vent passages 34. Thus, although the flow of working fluid through anvil exhaust duct 21 and upward in the well annulus will be stopped during these periods due to closure of exhaust duct 21, 22. by valve 39, substantial pressure pulsations will be produced through passages 34 which will tend to minimize the fluctuation of upward liuid flow about the tool and thus tend to keep the cuttings moving upwardly and maintain adequate support for the bore wall.

The effective force tending to drive the piston downwardly can be controlled by means of spring 4S. If, for instance, the compressive reaction of the spring is increased, as by increasing the thickness of bushing 1, the operating fluid can be supplied at greater pressure without causing premature unseating of valve 39 from piston seating element 35. On the other hand, if it is desired to supply drill fluid at a greater rate than is necessary to operate the percussion motor or to increase ow of drill fluid above that required to operate the motor, this can be achieved by reducing the compressive reactance of spring 48 or by increasing the pressure of the working fluid such that the motivating fluid pressure times the area of passage 31 (wb2/4) is greater than the reactive force of spring 48 plus the ambient well pressure times cross sectional area of the valve area (mi2/4), thus holding valve 39 away from seat 35. This will permit bypassing of some of the working fluid around valve 36 and thence through exhaust duct 21, 22 during the working stroke.

In gas drilling and in shallow wells, the reactive force of spring 48 is more effective than in deep wells where drilling mud is used. This is because in the latter case, the ambient pressure acting upwardly through ducts 2l, 22 upon valve 39 will greatly exceed the reactive force of spring 48. Also, in deep holes, the difference between the areas l1rb2/4 and mi2/4 becomes important as these areas determine the differential lacross the valve body 36. In general, this differential should be minimum where the spring is to be relatively more effective. A greater differential will increase the relative effect of ambient pressure, even to the point where the spring force may be negligible so that a very highly-loaded spring is not necesary, particularly in a deep well, to obtain quite large net operating pressures on the piston. Thus, the novel percussion motor may be used with gaseous or liquid motivating lluids and in shallow or deep holes, Iand higher operating pressures can be utilized simply by increasing the areasof the valve seating elements.

Normally, the piston does not contact bumper 11, except when the motor is not operating, as above explained. However, by decreasing the clearance between the under surface of the bumper 11 and the upper surface 51 of the piston, the piston can be caused to strike the bumper at the rear or upper end of each return cycle. With the bumper made of steel or other highly-resilient material, a very sharp turn-around expediting effect can be achieved. Since no valve action is involved during the turn-around between the returning and working strokes of the piston, such sharp bumper action has been found yadvantageous in increasing the frequency of hammer action. FIG. l shows in dot `and dash line at S5 the alternate extended position of bumper 11.

In the modification in FIG. 3, the valve seating element 57 in piston 26a is formed as a separate ring which is inserted Iagainst an inner shoulder 58 Within piston passage 31a and secured in position by a snap ring 59. An O-ring seal is provided at 60. Seat member 57 extends radially inwardly from the Wall of piston passage 31a and has a depending, relatively narrow valve engaging boss 61. The effect of this separate member 57 is to provide a reduced dimension b-l and, accordingly, the upwardly-facing surface area of valve 39a which is exposed to the working fluid pressure when the valve is seated on element 61. This, in turn, reduces the total force tending to open the valve and, therefore, permits the application of higher working fluid pressure to the hammer piston. In this form, seat element 57 may strike valve superstructure ange or collar 42a to unseat valve 39a from the anvil.

In FIG. 4, the valve 39b is provided with a bypass oritice 64 which provides for a constant supply of working fluid to the bit during operation. Alternatively, the same result can be achieved, as explained above, by increasing the Working pressure sufficiently to prevent the valve from engaging piston valve seat element 35. However, this would result in constant bleeding of drilling fluid past the seating element and where the -drilling uid is abrasive, erosion of the seating element would result.

La the form in FIG. 5, the valve 39e is equipped with an axial through passage 66 provided with a. transverse fracturable disk 67. If for any reason it is desired to bypass additional drill iiuid, as vin case the tool should become damaged or stuck, disk 67 can be fractured by a suicient increase in the working uid pressure applied thereto. The valve unseating stop ring 43 of the previous forms is omitted in this form. It has been found that in some cases the water hammer shock produced by irnpact of the hammer and seating of the motoring valve against the anvil decays suciently rapidly to produce an automatic pop off of the valve and avoid the necessity of the mechanical valve reversal.

In the modification of FIG. 6, stop ring 11a has its central passage 32a plugged at the bottom, as at 69, and the wall of the bumper is provided with inclined passages 70 which open through the bottom face of the bumper. The passages 70 are positioned to be sealed by the upper surface 51 of piston 26 in the rest position of the piston. This provides an additional seal for preventing the entry of contaminating and/or Vabrasive ambient well liquids into the drill motor. Also, the bumper may be mounted, as shown, on resilient ribs 72 for dampening the vibratory shock where the piston strikes the bumper at the rear end of each stroke to expedite the .turn-around. Also, it may be possible to construct the bumper of sufcient mass that no connection at lall need be provided with the casing, the bumper merely resting on a flange, for instance. Resilient ribs 72 may be secured in grooves or recesses in the surface of the piston.

The for-m in FIGS. 7, 8, `and 9 is intended to insure the reversal of the valve during the latter part of the return stroke of the piston more positively than in what I term the auto-pop means of FIG. 5, but by the use of hydraulic means rather than the mechanical means shown in FIGS. 1-4. Main valve body 75 has a rearwardly-facing, tapered part 76 for seating against the seat element 77 at the outlet of axial piston passage 78 in piston 91, and a forwardly-facing portion 79 for engaging seat element 80 about the inlet of exhaust duct 81 in the anvil. A generally tubular structure 82 projecting above the valve body slidably fits passage 78 and has -sector-shaped, longitudinal cutouts 83 located oppositely in its outer surface, a transverse passage 84 opening oppositely through ports 8S, and a longitudinal, central passage 86 connecting transverse passage 84 with anvil exhaust through duct 81. Projecting downwardly from the valve body and freely received in duct 81 is a skeletonized part S8 which rests at its lower extremity on a sleeve or bushing 89 which, in turn, rests upon coiled spring 90 supported upon a shoulder Within exhaust duct 81, as 51 in FIG. l.

In operation, during the latter part of the rearward stroke of piston 91, the outlet (forward) extremity of piston passage 7 8, which also forms valve seat 77, passes over ports in guide structure 82 (dot-dash lines in FIG. 7). The operating fluid, supplied through sector cutouts 83 to forward working chamber 93 to lift the piston, now is relieved through passages 84 and 86 so that the pressure across the valve is substantially equalized. Thereafter, spring 90 urges the valve seat 76 'against piston valve seat element 77 to reverse the piston movement and initiate the working stroke of the piston, as in the previous forms. When the piston strikes anvil 95, the valve is impelled downwardly by inertia, closing exhaust passage 81 in the anvil .and redirecting the Working fluid into forward working chamber 93 to repeat the cycle.

The form in FIGS. 10-14, inclusive, omits the valve actuating spring of the previous forms. Here, the valve body is in the form of a downwardlyand outwardlyinclined ring 96 having a periphera-l seating portion 97 which may be provided with a resilient seating part 98. A skeletonized structure 99 projects above the valve body and its upper end carries an external flange 100. A sleeve 1G11 is secured in the outlet portion of passage 102 in piston 103, as by means of .a snap ring 104 seated between a groove 105 therein and a tapered groove 166 in the piston bore, and a locking nut 104e. An annular, shoulder-'forming element 107 projects from the inner wall of sleeve 101 for eng-aging flange 100 to positively unseat valve 9'6-98 during the latter part of the return stroke of the piston. A plug element 108 is secured at the inlet of anvil exhaust passage 109 by means of parallel longitudinal legs 110 themselves secured in Vpassage 109 in anvil 111, as by a snap ring construction 112. A ring 113, preferably of resilient material, projects above the periphery of plug element 108 and has a tapered outer surface 114 for a purpose to be described.

This form operates as follows: FIG. 10 shows piston 103 after striking anvil 111 and after ring valve 96-98 has been impelled forwardly by inertia to seat against the anvil valve seating element 117. The working fluid then flows through skeletonized structure 99 and into forward working chamber 118 to impel the piston rearwardly.

After unseating of the valve from the anvil valve seat during the piston return stroke, as shown in FIG. l2, the static pressure of the operating iiui-d in space 120 between plug 108 and valve 96 applies a lifting force to valve part 96, as indicated lby the arrow. At the same time, the working fluid will ow at considerable velocity through space 121 into forward Working chamber 118 to aid in lifting the piston and also through clearance 123 beneath motoring valve 96-98. Due to the wire drawing effect of the flowing operating fluid in space 121, the static pressure therein will be substantially less than that in space 120 so that the motoring valve will lbe impelled upwardly, as shown in FIGS. l2, 13, and 14. Since the pressure on the forward end of the differential piston will be substantially reduced upon lifting of the valve from anvil seat 117, the piston return stroke will be halted and its power stroke begun. When the piston strikes the anvil, as in FIG. l0, the operating valve is irripelled forwardly by inertia to repeat the cycle. Valve 96 may seat on sleeve 101, as in FIG. 14, just before the piston strikes the anvil.

The nal form in FIGS. l5 and 16 is for the purpose of reducing the area of the operating valve exposed to operating pressure, as also achieved in FIG. 3. However, in this form, a cup-like nipple member 126 is secured by means of a snap ring 129 at the outlet end of a sleeve 127 lodged in piston 4passage 128. A resilient packing A13:0 may be interposed between the sleeve and nipple 126. Ports 131 are formed in the skirt of memer 125 just below the lower extremity of sleeve 127. The bottom 132 of the nipple member is provided with a central aperture 133 in which is slida'bly received the shank portion 134 of a bolt whose enlarged head 135 normally rests -on the upper surface of the nipple bottom part. A nut 136 is provided on the free lower end of the bolt and suitably secured in position.

A ring valve of angular section has an apertured transverse web 137 received about bolt shank 134 .and lan upstanding peripheral part 138, the inner surface 139' of 4which slides on the exposed outer surface of nipple member 126, sealing grooves being provided in the mating surface of this member. At the upper end of upstanding valve part 13S there is provided a tapered seat 140 which may engage a corresponding seat element 141 at the lower end of sleeve 127. At the bottom edge of upstanding valve part 138, there is provided atapered seating portion 142 which may cooperate with a seating element 143 about the inlet of exhaust passage 144- in anvil 145. A skeletonized guide sleeve 14.6 depends from valve part 138 and its lower extremity rests upon a spring seat ring 147 which, in turn, rests upon coiled spring 148.

'When this form is subjected to pressured operating fluid, with ring valve 138 in its upward position to close ports 131 (FIG. 16), the operating fluid, being now restricted to the rear or upper end of the piston, drives the piston forwardly in its working stroke. However, the ring valve in this form is substantially relieved of the operating fluid pressure, except that applied laterally through ports 131, so that a relatively light spring 148 may be used. When the piston strikes the anvil, the ring valve is impelled downwardly by inertia to seat against the anvil, as shown in FIG. 15. Now, the operating tluid is directed through ports 131 into the forward Working chamber to drive the piston rearwardly, the working pressure also tending to hold the ring valve on its Seat 143. During the latter part of the piston return stroke, nut 136 engages transverse part 137 of the ring valve to positively unseat the same from the anvil, whereupon spring 148 urges the ring valve again against its seating on sleeve 127 and so as to close ports 131. This reverses the piston action and initiates the working stroke. This form, of course, has the advantage that the working pressure can be greatly increased without the necessity of providing an unduly heavy valve actuating spring 148. The valve may be actuated wholly hydraulically, as in FIGS. 10-14, and the structure for positively unseating the valve from the 4anvil may be substantially varied.

The novel drill motor, in its several forms, is very flexible .as to pressures and volumes of the working tluid as well as the kind of working fluid it will accommodate. Where the valve closes fully against the hammer seating element during the turn-around and down stroke, the Vworking stroke will be impelled most eiiiciently by positive displacement. In such operation, the use of the differential area piston results in transfer of energy from the moving uid to the hammer with minimum surges in the drill pipe and annulus. Since energy will be transferred at a pressure level that satisfies the inertial eqn-ation y(force equals mass times acceleration) and since the pressure times area equals the driving force, it follows that the working pressure must increase Ias the area decreases. However, the surge or shock pressure is represented by the equation P=PCr where PS=Shock pressure at turn-around P=the speed of sound in the medium (piston steel) r=velocity of the piston This shows that the shock pressure will increase as the piston area exposed to the working pressure decreases. Accordingly, the reduced upwardly-facing .area of `the piston results in greater surge or shock pressure and more rapid turn-around.

At both extremes of movement of the hammer piston the full water hammer surge develops due to the momentary stopping of the operating fluid ow. Upon striking lof the hammer, the surge pressure acts upon the full exposed `area of the valve and keeps the valve closed on the anvil against the heavy spring thrust.

The valve design is important and it is preferred that the area of the valve radially outside of the hammer valve seating element 'be reduced as 4much as possible so that the increased area exposed to the working fluid, as tlte valve opens downwardly, is reduced to Ia minimum. Thus, the action of the valve as a pressure costroler is more eiiicient and the valve responds to closely-varying pressures, thus reducing or eliminating the need for an accumulator or da'mpener in the operating iluid line and also reducing the shock to the rig. Another advantage of most of the forms of the novel valve is that they are not guided by any sliding contact with other parts, but rather' tloat in the operating medium so that the valve tends to have the same velocity as the hammer at the time the hammer strikes the anvil. Furthermore, there is no need for any means other than inertia to assist the valve action at the end of the working stroke. At the rear end of the stroke, the turn-around may be mechanically triggered or may rely on changing of fluid for-ces.

During the time of the impact upon the anvil and the return stroke of the piston, the pressure within the anvil land on the drilled roei: face is advantageously reduced. This reduces the restraining pressure on the chips being produced making it easier for the chips to ily and requiring less blow energy to trigger the activity. This reduced pressure zone, however, does not affect uphoe conditions materially, since the surge wiihin the hammer acts to accelerate the hammer upward from its impact position causing an upward fluid impulse in the vented space 33 and the well annulus.

It is contemplated that the spring and vaive will be supplied as a separate assembly which can be replaced as wear occurs or as it is desired to alter the manner of operation or the type of working fluid used. The separate valve seating insert in the piston contributes rnaterially to the flexibility of the tool. Of course, a special anvil-bit must be provided for use with this new tool.

When the tool is lifted off bottom, the spring load on the valve is reduced, duc Ato dropping of the anvil relative to the casing. While the piston is stopped by ring S5, valve 26 would then seat against piston seat 35 to resist access of well fluid into the tool. In order to produce blowing of the -drill fluid under such condition, it is only necessary to increase the delivery pressure thereof suicient to force the valve off seat 35. On the other hand, with the springless form of FIGS. 10-14, the ring valve functions more or less as an ordinary check type oat valve. Whether the tool is drilling on bottom or is suspended olf bottom, if there is a predetermined rise in Well fluid pressure, the valve will close up on its piston seating element and lift the piston to engage the bumper, thus shutting off the drill pipe from the well liquid. Further, when a round trip is being made, with the tool in suspended position, the pressure setting of the control valve is reduced allowing the valve to Open and the liquid in the drill stem to run into the well. Thus, dry pipe will be handled on the rig platform.

The invention may -be modified in various respects as will occur to those skilled in the art, and exclusive use of all modifications as come within the scope of the appended claims is contemplated.

I claim:

1. In a percussion drill having a casing with a forward part of greater transverse area than the rear part thereof, a hammer piston re-ciprocable in said casing and having 4differential forward and rearward working faces received respectively in said casing forward and rear parts, there lbeing a longitudinal passage extending through said piston, a connection for supplying operating fluid to said casing rear part under normal -operating conditions, and an anvil in said ICasing forward part with an exhaust duct therethrough, the improvement comprising rst and second opposinU valve seats respectively at the radjacent ends of said longitudinal passage and said exhaust duct, a check valve received between said seats, and means operable on said valve for impelling the same towards said rst seat, under normal operating conditions, during the latter part of the rearward return stroke of said piston for restricting said piston passage and exhausting said casing forward part through said anvil duct and thereby initiating the forward power stroke, said valve impelling means Ibeing calibrated and said valve being of suflicient mass to cause said valve to be impelled forwardly against said anvil seat, upon striking of the anvil by said piston, t-o clear said piston passage and close said exhaust duct and thereby initiate the return stroke lof the piston.

2. In a fluid operated percussion drill, a casing, an anvil at the forward end of said casing having an exhaust duct, a piston reciprocable in said casing for beating upon said anvil, said piston having a longitudinal passage therethrough and having a forward working face which is larger than the rearward working face thereof, and a connection at the rear end of said casing for constantly supplying operating fluid to said piston rear face and forwardly through said piston passage under normal operating conditions, the improvement comprising opposing piston and anvil valve seats at the adjacent ends of said piston passage and said exhaust duct, a double acting check valve having seating parts movable between and cooperable with said seats, and means for impelling said valve toward said piston valve seat under normal operating 'conditions during the latter part of the rearward return stroke of said piston while opening said exhaust duct to said casing forward part for producing the forward power stroke of said piston, said valve seats being spaced apart axially of the drill -a greater distance than said seating parts and said valve impelling means being calibrated and said Valve being constructed and arranged to cause said piston to be impelled against sa-id anvil seat, when said piston strikes said anvil, to close said exhaust duct land open said piston passage to said casing forward part and thereby produce the return stroke of said piston.

3. In a percussion drill having a casing, a connection for `supp-lyinU operating fluid to the rearward part of said casing and an anvil at the forward part thereof, a hammer piston reciprocable in said casing to beat upon said anvil, the forwardly-facing area of said piston being exposed to the forward part of said casing and being greater than the rearwardly-facing area thereof, passage means leading from said connection to the forward part of said casing, an exhaust duct leading from said casing forward part, the improvement comprising valve seat elements, respectively, in the `outlet of said passage means and the inlet of said duct, valve means movable between said seat elements, and means for alternately causing seating of said valve `means on said exhaust duct and passage -means seat elements to thereby cause successive application of the -oper-ating fluid pressure through said passage seat element to said piston forwardly-facing area, while said exhaust duct seating element is closed, for impelling said piston rearwardly, and for closing said passage seat element to exclude said iiuid pressure from said forward piston area while exhausting said forward casing part through said exhaust duct seat element to cause said piston to -beat upon s-aid anvil.

4. In a tluid operated percussion tool, a casing, an anvil at the forward part of said casing with an exhaust duct, a diiferential piston working in said casing with its forward Working face larger in transverse area than its rearward working face, a connection at 'the rear end of said casing for supplying working fluid to the rearward part of said casing, and a longitudinal passage through said piston, the improvement comprising opposing piston and anvil valve seats, respectively, at the adjacent ends of said piston passage and anvil duct, a unitary, double-acting check valve floating between said seats, and means to maintain said valve against said piston seat during normal operation in the latter part of the rearward return stroke and during the forward Working stroke of said piston to cause said working stroke, said valve maintaining means being calibrated and said valve being constructed and arranged to cause said valve to be impelled forwardly by inertia upon striking of said anvil by said piston to close said anvil exhaust duct and again expose said larger piston forward surface to the working fluid to repeat the cycle.

5. A percussion drill as described in claim 4 in which said means maintaining said valve means against said piston seat includes a spring stressed between said valve and said anvil.

6. A percussion drill as described in claim 4 in which said valve means comprises a one-piece valve body having upper and lower seating faces for cooperating alternately With said seating elements.

7. A percussion drill as described in claim 6 further including cooperating structures projecting, respectively, from said valve body and the wall of said piston passage for unseating said valve body from said exhaust duct seat element during the return stroke of said piston.

8. A percussion drill as described in claim 7 further including spring seat and guide structure depending from said valve.

9. A drill as described in claim 5 further including an internal shoulder in said exhaust duct and spring seating and guiding structure depending from said valve means, said spring being stressed between said shoulder and said structure.

10. A percussion drill as described in claim 4 in which said piston valve seat constitutes a substantial restriction in said piston passage to reduce the area of said valve exposed to the operating uid during the working stroke and thereby reduce the force necessary to maintain said valve on said piston seat during the working stroke.

11. A percussion drill as described in claim 10 in which said passage valve seat is separately formed and replaceable for repair purposes and to adjust the area of said valve means exposed to the operating fluid pressure when said valve means is seated on said passage seat element.

12. A percussion drill as described in claim 4 further including a stop member in the rear part of said casing positioned to limit rearward movement of said piston but to clear said piston during normal reciprocation thereof.

13. A percussion drill as described in claim 4 further including a highly-resilient stop member at the rear end of said casing in position to be engaged by said piston at the rear end of each normal return stroke to expedite the turn-around of the piston.

14. A drill as described in claim 12 in which said connection for operating fluid includes port means opening through said stop member in position to be closed by said piston when in engagement with said member for sealing communication through said casing.

15. A drill as described in claim 4 further including a constantly open bypass opening through said valve body.

16. A percussion drill as described in claim 4 in which said check valve includes structure projecting into said piston passage and recessed to direct operating uid from said piston passage into the forward part of said casing when said valve is on said anvil seat, said structure having a bypass duct positioned to be closed :by said piston when Asaid valve initially engages said anvil seat and to be exposed beneath said piston vduring the return stroke thereof for bypassing uid in said casing forward part into said anvil duct to relieve the pressure in said casing forward part whereby said check valve may close against piston valve seat -to initiate the working stroke of the piston.

1'7. A percussion drill as described in claim 16 in which the means for urging said valve against said piston valve seat comprises a spring compressed between said valve and the anvil.

18. A percussion drill as described lin claim 4 in which said anvil exhaust duct opens into said casing forward part through an annulus about a central plug, said anvil valve seat being formed at the outer edge of said annulus, and said check valve having radially-spaced inner and outer annular parts for seating respectively on said piston and anvil valve seats and an upwardly and inwardly disposed wall structure between said parts, the under surface of said wall structure 'being of greater area than the valve area exposed to the operating fluid when said valve is on said piston seat whereby the operating fluid trapped between said under surface and said plug urges said valve toward said piston valve seat.

19. A percussion drill as described in claim 18 in Awhich the upper surface of said upwardly and inwardly disposed wall structure is exposed to wire drawing effect due to flowing of operating uid lbetween the same and said piston during valve movement from said anvil seat to said piston seat for assisting in said movement.

20. A percussion drill as described in claim 13 further including cooperating structure on said valve and said piston for positively unseating said valve from said anvil seat during the latter part of the rearward piston movement.

21. in a percussion drill having a casing, an anvil at the forward end thereof with an exhaust duct, a differential hammer piston reciprocable in said casing for beating upon said anvil, a longitudinal passage through said piston, and a connection with the rearward portion of said casing for supplying operating uid thereto, the improvement comprising a valve seat on said anvil about the entry of said exhaust duct, a nipple member depending from the lower face of said piston and having a closed bottom and port means in the side wall thereof, a ring valve slidable on said nipple, and means for urging said ring Valve to a rearward position during the latter part of the piston rearward movement for closing said port means to substantially confine the operating fluid to the upper surface of said piston and thereby drive said piston forwardly, said valve being constructed and arranged to be impelled forwardly by inertia when said piston strikes said anvil for seating against said anvil to close said anvil exhaust duct and direct operating fluid into said casing forward part and thereby cause the rearward movement of said piston.

22. In a percussion drill having a casing with an operating fluid connection at its rear end and an anvil at its i;

forward end having an exhaust duct therethrough, a differential hammer piston in said casing, a longitudinal passage through said piston, waiving means controlling said CII p 12 longitudinal piston passage and said exhaust duct to cause said piston to beat upon said anvil under the influence of operating fluid supplied through said connection, said casing having an enlarged lower part slidably receiving an enlarged lower part of said piston and forming therewith a clearance space, a first predetermined portion of which is periodically filled and evacuated by said piston forward part during operation, the improvement comprising a charge of fluid in said clearance space which is substantially non-damaging to said piston and casing, vent means between a second portion of said clearance space and the exterior of said casing, the effective capacity of said vent means being sufficiently greater than the volume of said first fiuid pumped by said piston during operation to prevent the drawing of said ambient fluid into said clearance space.

23. A percussion drill as described in claim 22 in which aid firs-t fluid is relatively immiscible with said ambient well fluid and said vent means is of suicient length to retain the parting line between said fluids therein.

24. An anvil-bit device for a percussion tool having a rear part for slidable reception in a percussion tool casing and an axial exhaust passage for operating fluid, a valve seat about the inlet of said passage for cooperation with a motoring val-ve, and a shoulder within said passage for seatin a motoring valve operating spring.

25. An anvil-bit device for use with a percussion drill having a casing and a hammer piston reciprocable therein, said device having a forward, formation cutting part, a rear part for slidable reception in the forward end of the drill casing, an axial exhaust duct with an enlarged inlet, a motoring valve seat about said inlet, and motoring valve biasing means in said inlet.

References Cited UNITED STATES PATENTS 1,333,725 3/1920 Newbert 173-139 X 2,403,582 7/1946 Caudill 173-137 X 2,861,778 11/1958 Spurlin 173-139 X 3,040,710 6/ 1962 Wilder 173-78 X 3,101,796 8/1963 Stall et al. 173-73 3,162,251 12/1964 Bassinger 173-73 3,327,790 6/ 1967 Vincent et al 173-73 1,861,042 5/1932 Zublin 175-296 X 2,344,725 3/ 1944 Phipps 175-296 2,580,203 12/ 1951 Topanelian 175-296 X 2,758,817 8/1956 -Bassinger 175-296 NILE C. BYERS, JR., Primary Examiner.

FRED C. MATTERN, Examiner'.

L. P. KESSLER, Assistant Examiner. 

